Coating on Duplex Underground Pipeline 1

[Vinzzzz]

Dear all,

is it right to coat an Underground Pipeline in duplesx material type S31803? I'm doing a project in Algeria for a gatering system to construct so the soil is prevalently constituted by sand. I suppose that corrosion mechansms could be done by differencial aeration or electrolites presence, but in the same time this material should be projected to resist to these environments.
In case of Cathodiic protection obviously i opt for a coating system in order to reduce current density demand.
In case of is always suitable coat the duplex pipeline which could be the coating system suitable for the scope? could Polyethylene or Polypropylene be suitable for the scope? I'm oriented on Polypropylene system coat of 3 mm in thickness.

Regards Vincenzo

 

[SJones]

Yes, it is right to coat an underground duplex SS pipeline for at least the two reasons that you have stated. The choice of coating depends on a number of parameters, not least pipeline operating temperatures and available applicators. Take a look at the new ISO 21809-1 to help you choose between PE and PP, but other coatings could also feature, so hunt around around for appropriate standards.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[Vinzzzz]

Dear Steve,

many thanks for your reply. Client have decided for PP coating but anyway I will follow your advice principally for my knowledge.

I have another question for you, I have seen on ASTM for Pipe material A790 Grade S31803 that pipes, obviously, shall be fournisced in pickled conditions without any type of spot.

My question is the following
is rigth to require also the passivation treatment after pickling?

On ASTM is not mensioned the passivation, probably because we are speaking about a duplex material where the Cr quantity is to high that in a short time it will form a protective stable and uniform superficial oxide. Anyway in my opinion I will ask for a passivation treatment to the pipes supplier in order to be sure that the external layer will be omogeneus.

Thanks for all.

With my best Regards

Vincenzo

 

[EdStainless]

Passivation is not truly to form a better passive layer, it is to clean the surface so that the SS can form a uniform passive surface.
It should not be necessary to passivate this pipe.

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Plymouth Tube

 

[SJones]

Indeed - it has just become the norm to have 'pickle and passivate' together. It only need be one or the other - see the attached.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04